This invention relates to an image formation apparatus such as a copier or a printer and more particularly to an improvement to enable an image to be formed appropriately on not only a transfer material of a single composition such as paper or an OHP sheet, but also a transfer material of a multilayer structure such as a tack film, cloth paper, or a transfer material formed with a bonding layer.
For example, available as a conventional image formation apparatus for forming an image on a transfer material is an electrophotographic color image formation apparatus having an image support on which toner images of primary colors are formed in sequence in response to image information, transfer charge means being placed facing the image support, to which a predetermined transfer voltage is applied, a transfer material support being disposed rotatably so as to pass through a transfer position between the transfer charge means and the image support, a transfer tray for storing transfer materials, attraction charge means for electrostatically attracting a transfer material discharged from the transfer tray on the transfer material support, static elimination charge means for weakening the attraction force between the transfer support and the transfer material by static elimination, a peeling claw for peeling the transfer material subjected to the static elimination from the transfer material support, and a heating roll and a pressurization roll for heating and pressurizing the peeled transfer material.
The image formation apparatus thus configured charges the transfer material support and the transfer material by the attraction charge means, thereby attracting the transfer material on the transfer material support, then forms toner images of different colors on the image support in sequence and transfers the toner images to the transfer material by a transfer electric field in sequence for forming a multicolor toner image, then peels off the transfer material from the transfer material support by the static elimination charge means and the peeling claw and heats and pressurizes the peeled transfer material by fixing means for fixing the image on the transfer material, thereby forming the image on the transfer material.
By the way, the image formation apparatus for forming an image on a transfer material in such a manner, as seen from the fact that it is recognized as an office automation machine, has been developed as an apparatus for preparing general documents in offices. That is, such an image formation apparatus generally forms images on plain paper and OHP sheets; even a high-performance model brought to the commercial stage in recent years is only improved so that it can form an image at most on a standardized card such as a postcard.
Then, in response to an improvement in the image quality of image formation apparatuses or passable accomplishment of color image formation apparatuses in recent years, the inventors et al. tried forming an image on various transfer materials not intended formerly as transfer materials by image formation apparatuses, for example, transfer materials of a multilayer structure, such as tack films, cloth paper, and transfer materials formed with a thermally melted bonding layer. However, the result was poor; an image of proper quality can be formed on the transfer materials or the transfer materials cannot be transported from a paper tray to a discharge tray. The following problems are problems not arising when images are formed on plain paper, etc.,:
As a first general problem, in some cases, a transfer electric field produced at a transfer position or a transfer current flowing at a transfer position changes with transfer materials of a multilayer structure and toner on an image support cannot be appropriately transferred to the transfer material. Particularly, in the second or later transfer, no toner is transferred in some cases; an image degradation problem in color images is marked.
As a general problem at a fixing position, a transfer material of a multilayer structure and whole toner cannot be sufficiently heated because of the thickness of the transfer material of a multilayer structure and the color development property worsens in color images, etc.,; in an extreme case, only toner on the surface of multicolor toner image is melted and no image is fixed. Particularly, when only toner on the surface of multicolor toner image is melted on a highly insulated transfer material such as a tack film, the melted toner is deposited electrostatically on the surface of a heating roll and an image can be made dirty to such a degree that it cannot be distinguished with eyes at the next fixing time (this problem will be hereinafter referred to as "nonvisual offset").
As a general problem related to transport of transfer materials, in some cases, the attraction position of a transfer material on a transfer material support shifts, a transfer material cannot appropriately be attracted on a transfer material support, or a transfer material cannot appropriately be peeled off from a transfer material support.
Although the following problems do not generally occur in transfer materials of a multilayer structure, as a hindrance to image formation, first if an image is formed on a lowly insulated transfer material of a multilayer structure, the transfer material is attracted on an image support, etc., at a transfer position or an attraction position at a considerable probability and further if a transfer material is luckily peeled off from an image support at a transfer position, the image support is charged up by peel discharge associated with the peeling and a toner band is formed on the next image.
If an image is formed on a transfer material formed on a surface with a coating under a damp condition, toner or moisture absorbed on the transfer material at a fixing position becomes water vapor at the fixing time and cannot escape, thus a missing image occurs as the water vapor is broken, which will be hereinafter referred to as toner blister, or a part of the coating is peeled off from the base material of the transfer material, which will be hereinafter referred to as paper blister.
When the electrophotographic color image formation apparatus is used to form an image on a transfer material, if the transfer material to which a toner image has been transferred is made to take a round with the transfer material held on the transfer material support, which will be hereinafter referred to as dummy cycle, and meanwhile the transport speed of the transfer material is slowed down for improving the fixing property, a part of toner is retransferred from the transfer material to the image support during the dummy cycle and image quality defects such as tone change occur.